Bacterial genetic techniques will be used to investigate the mechanism by which molecules of the RecA protein of the bacterium Escherichia coli polymerize around DNA to form an active nucleoprotein complex. Proper formation of this complex is essential to the processes of DNA repair and DNA recombination, both of which are necessary for survival. RecA is closely related to similar proteins found in cells of higher organisms, including humans. This work is relevant to human health because defects in DNA recombination and repair in humans usually lead to cancer or severe genetic disorders. A deeper understanding of these processes may help in the development of treatments and diagnostic techniques for these specific illnesses. [unreadable] [unreadable] The genetic technique of mutant-suppressor pair analysis will be applied to this problem. This involves the targeting of a mutation to one member of a pair of interacting proteins, and then seeking second mutations in the other member of the pair that reverse the effect of the first mutation. Mutant pairs such as this are very useful in mapping individual amino acid contact points between interacting proteins. To implement this strategy, an altered form of the RecA polymer will first be generated. This will done by obtaining pair of recA mutants that are each unable to polymerize by themselves, but are able to interact with each other to form fully functional polymers. These polymers will be characterized by alternating interface specificities. [unreadable] [unreadable]